The invention relates in general to x-ray or gamma ray detectors and in particular to blocking contacts on such detectors.
Cadmium Zinc Telluride (CdZnTe) has gained acceptance as a semiconductor detector material for x-ray and gamma ray applications ranging from astronomy to medical imaging. One challenge remaining for this technology is the production of large volume (greater than 4 cubic centimeters) detectors free of bulk defects (grain and twin boundaries), which are detrimental to detector performance. CdZnTe can be produced by several different Bridgman furnace configurations, for example High Pressure Bridgman (HPB) or Modified Horizontal Bridgman (MHB).
The HPB process produces slightly p-type CdZnTe with a very high bulk resistivity (1011 Ohm-cm) and, therefore, these detectors have low leakage current noise and good spectral performance. Unfortunately, HPB CdZnTe has a high density of bulk defects that results in a poor yield and high cost for large volume detectors. The MHB growth process produces n-type CdZnTe with a much lower density of bulk defects. However, the material has a relatively low bulk resistivity (5×109 Ohm-cm) and, therefore, conventional ohmic contacts yield much higher leakage current noise resulting in a poor spectral resolution. To take advantage of the lower density of bulk defects in MHB CdZnTe, there is a need for contacts having low leakage current noise.